Self-Amplifying RNA Vaccines After the First Approvals: Technology, Development Landscape, and Regulatory Science Considerations

Self-amplifying RNA (saRNA) is a next-generation nucleic acid vaccine platform that enhances antigen expression through intracellular amplification of replicon RNA without producing infectious virions. saRNA constructs encode an alphavirus-derived replicase comprising nonstructural proteins nsP1–nsP4 and can elicit robust immune responses at low RNA doses. Replication intermediates may activate RIG-I, MDA5, and endosomal TLR3/7/8, contributing adjuvant-like activity. Kostaive (ARCT-154; zapomeran) became the first saRNA vaccine to receive full marketing approval in Japan in 2023, followed by authorization in the European Union in 2025 and the United Kingdom in 2026, demonstrating the platform’s clinical and regulatory feasibility. Development now extends beyond COVID-19 to seasonal and pandemic influenza, rabies, Crimean–Congo hemorrhagic fever, Nipah virus disease, and individualized cancer vaccines. However, the longer transcripts and additional replicase and subgenomic-promoter elements make in vitro transcription efficiency, full-length RNA content, double-stranded and truncated RNA impurities, lipid nanoparticle encapsulation, and potency testing particularly important. Regulatory assessment increasingly focuses on correct replicase and antigen expression, the magnitude and duration of self-amplification, biodistribution and persistence, and comparability. This review synthesizes the scientific basis, development landscape, manufacturing challenges, and regulatory science considerations of saRNA vaccines.